The Sprained Ankle

Introduction

The sprained ankle is the most common musculoskeletal injury seen by physicians caring for active children and adults. It accounts for approximately one-fourth of all sports-related injuries and is commonly seen in athletes participating in basketball, soccer, or football. While diagnosis and management of the sprained ankle is usually straightforward, several serious injuries can masquerade as an ankle sprain, and it is important for the clinician to recognize these to prevent long-term morbidity.

Anatomy

The bony ankle mortise is formed by the tibial plafond and the medial and lateral malleoli. This articulates with the body of the talus and forms the talocrural joint. The configuration of the talus is such that when its wider anterior portion is positioned within the mortise when the ankle is dorsiflexed, relative bony stability is greatest.

Conversely, when the ankle is plantarflexed, the narrower posterior portion of the talus is within the mortise and less bony stability is created. The inferior portion of the talus articulates with the superior portion of the calcaneus forming the subtalar joint. The majority of inversion and eversion of the hindfoot takes place at this articulation.

Lateral ankle stability is provided by 3 ligaments: the anterior talofibular ligament (ATF), the posterior talofibular ligament (PTF), and the calcaneofibular ligament (CF) (Figure 1).

Ankle

Figure 1. Anatomy of the lateral ankle.

The anterior talofibular ligament (ATF) originates from the anterior border and tip of the lateral malleolus and travels obliquely forward to insert in the neck of the talus. It is the primary restraint against inversion and torsional stress with the foot in plantarflexion.

The calcaneofibular ligament (CFL) extends from the tip of the lateral malleolus to the lateral calcaneus. It lies deep to the peroneal tendons and is closely associated with their tendon sheath. It is the primary restraint against inversion and torsional stress with the foot in dorsiflexion.

The anterior talofibular ligament and the calcaneofibular ligament act synergistically to provide stability to the lateral ankle. When the foot is in dorsiflexion, the anterior fibers of the calcaneofibular ligament are taut and the anterior talofibular ligament is lax. Conversely, when the foot is plantarflexed, the calcaneofibular ligament is lax and the anterior talofibular ligament is taut.

Medial ankle stability is provided by the deltoid ligament (Figure 2). This ligament complex is composed of 4 individual ligaments that blend together to form the deep and superficial portions of this ligament. They include the anterior talotibial ligament, the posterior talotibial ligament, the tibiocalcaneal ligament, and the tibionavicular ligament.

Ankle

Figure 2. Anatomy of the medial ankle.

The integrity of the ankle mortise is maintained by the syndesmosis between the tibia and the fibula. The anterior and posterior tibiofibular ligaments, the transverse tibiofibular ligament, and the interosseous membrane are the components of the syndesmosis that maintain the stability of the tibia and the fibula. Subtalar joint stability is maintained by the calcaneofibular ligament, the cervical ligament, the interosseous ligament, the lateral talocalcaneal ligament, and the ligament of Rouviere.

Mechanisms of Injury

Lateral ankle sprains account for the overwhelming majority of ankle injuries. These sprains usually occur as a result of landing on a plantarflexed and inverted foot.

When the ankle is unweighted, it rests in a position of plantarflexion and inversion. If the ground or an object is met unexpectedly when the foot is unweighted, the lateral ankle ligamentous complex may be injured. This may occur when running on uneven terrain, stepping in a hole, or landing on another athlete's foot after jumping. Studies have shown that plantarflexion/inversion injuries result in predictable injury to the lateral ankle ligamentous complex.

The anterior talofibular ligament is injured first, followed by injury to the calcaneofibular ligament and posterior talofibular ligament. Since the anterior talofibular ligament is the weakest ligament in the lateral ankle complex, it is most commonly injured as a result of plantarflexion and inversion injuries. However, if the force is great enough, the stronger posterior talofibular and calcaneofibular ligaments can be injured as well.

When the foot is dorsiflexed and inverted, the calcaneofibular ligament is injured. When the foot is in dorsiflexion and an external rotation force is applied, the syndesmosis is commonly sprained. With an eversion/external rotation injury, the strong deltoid ligament is injured.

EVALUATION

Injury History

Given the predictable injury patterns described above, a carefully taken history will elicit the mechanism of injury and provide valuable clues as to the ligamentous structures that may be injured. For example, an athlete who steps in a hole while running on uneven terrain will most likely suffer a plantarflexion/inversion injury and damage the anterior talofibular ligament.

On the other hand, an anterior lineman who has a teammate land on the back of his ankle while his foot is externally rotated will suffer a dorsiflexion/external rotation injury with suspected damage to the syndesmosis.

Other important historical features to obtain from the athlete include whether there was a perception of a "pop" at the time of injury; whether the athlete was able to continue to play after the injury; whether the athlete was able to bear weight on the ankle after the injury; and the time elapsed before swelling ensued.

A history of ankle injury or an inadequately rehabilitated ankle that has been previously injured are other features that should be important to note.

Physical Examination

The physical examination should be systematic and thorough and should include careful observation of the ankle for swelling, deformity, and ecchymosis. After observation, careful palpation of the lateral and medial malleoli, the tibiofibular syndesmosis, the anterior talofibular ligament, the calcaneofibular ligament, and the deltoid ligament should be performed.

Additionally, the base of the fifth metatarsal, the anterior process of the calcaneus, the lateral and posterior processes of the talus, and the peroneal tendons should be palpated since injuries to these structures may mimic an ankle sprain. The point of maximal tenderness should be determined and then provocative maneuvers performed to determine the stability of the ankle.

The first of these maneuvers is the anterior drawer test (Figure 3). This test assesses the integrity of the anterior talofibular ligament and measures anterior translation of the talus within the mortise. The test is performed by stabilizing the lower extremity with one hand and grabbing the heel with the other. The examiner then attempts to pull the talus forward within the mortise. Normally, the talus may translate 2 to 9 mm anteriorly, so it is important to compare the injured ankle with its non injured counterpart to determine whether there is a difference between anterior translation on the injured versus the non injured side. A positive test is determined by a 4-mm difference in anterior translation between the injured and the uninjured ankle.

Ankle

Figure 3. Anterior drawer test to evaluate the anterior talofibular ligament.

The talar tilt test assesses the competency of the calcaneofibular ligament (Figure 4). It attempts to assess the angle described by the tibial plafond and the dome of the talus when the ankle is inverted. Wide variability exists in the degree to which the normal ankle may be inverted, with normal values ranging from 5° to 23°. Again, the uninjured side must be examined for comparison. A positive test is defined as a 6° difference between the injured and uninjured sides. Because of the wide degree of variability in this test, its reliability is poor; it is not as reliable as the anterior drawer test.

Ankle

Figure 4. Talar tilt test to evaluate the calcaneofibular ligament.

The integrity of the syndesmosis can be assessed by performing the external rotation stress test. This test is performed by stabilizing the distal lower extremity with one hand while the other hand is used to externally rotate the foot with the ankle in plantarflexion. If the patient complains of syndesmosis pain with external rotation of the foot, the test is considered positive.

Ankle

Finally, the integrity of the peroneal tendons can be tested. The peroneus brevis and peroneus longus travel behind the posterior aspect of the lateral malleolus. They are kept in place by a fibrous retinaculum that can be torn or injured. If this occurs, the tendons can sublux from the groove in which they sit in the posterior aspect of the lateral malleolus. This can be assessed by stabilizing the lower extremity with one hand with the other hand placed behind the heel. The foot is placed into dorsiflexion and eversion. An anterior force is then applied, which may reveal the subluxation of the tendons over the lateral malleolus. The physical examination should be completed by performing a careful neurovascular assessment of the distal foot.

After the physical examination is performed, the severity of the ankle sprain can be graded. Grading the ankle sprain guides treatment and rehabilitation and also can provide useful information with respect to the expected time of disability. The West Point Ankle Sprain Grading System provides a useful schema for classifying injury and is depicted in Table 1.

Table 1. The West Point Ankle Sprain Grading System

 
  Criteria Grade 1 Grade 2 Grade 3
 
  Location of tenderness ATFL ATFL, CFL ATFL, CFL, PTFL
 
  Swelling & Ecchymosis Slight, localized Moderate, localized Significant, diffuse
 
  Weight bearing ability Full weight bearing, Partial WB Difficult without crutches Impossible without pain
 
  Ligament damage Stretched Partially torn Completely torn
 
  Instability None None - slight Definite
 

On average, Grade 1 injuries will result in 7 to 14 days lost from activity, while Grade 2 sprains may result in a loss of anywhere from 2 to 6 weeks of activity. Grade 3 sprains may result in a loss of as few as 4 weeks to as many as 26 weeks from athletic competition.

Radiography

After the injured ankle has been carefully assessed, the need for radiographs should be determined. The development of the Ottawa ankle rules has dramatically reduced the ordering of unnecessary x-rays while reliably identifying important bony injuries. These rules are very easy to apply.

If there is pain near the medial or lateral malleolus and the patient is unable to bear weight immediately and at the time of evaluation or if there is bony tenderness at the posterior edge or tip of either malleolus, then ankle x-rays (3views) should be obtained.

Likewise, if there is pain in the midfoot and an inability to bear weight immediately and at the time of evaluation or if there is bony tenderness at the navicular or at the base of the fifth metatarsal, foot films (3views) should be obtained.

It is important to note that these decision rules were studied in the emergency department setting. In the athletic setting, the additional likelihood of syndesmosis injury is high; therefore, many clinicians have added syndesmosis tenderness and a positive external rotation stress test as additional criteria that should lead to radiographic examination of the ankle.

Differential Diagnosis

Before treatment can begin, an accurate diagnosis must be made. It is important to consider the differential diagnosis of the acutely injured ankle so that serious injury that may mimic an ankle sprain can be excluded. The differential diagnosis of the acutely injured ankle is presented in Table 2.

Table 2. The differential diagnosis of the acutely sprained ankle.


  1. Sprained ankle
  2. Physeal fractures
  3. Osteochondral fractures
  4. Lateral process fracture of the talus
  5. Posterior process fracture of the talus
  6. Anterior process fracture of the calcaneus
  7. Fracture of the base of the fifth metatarsal
  8. Fracture of the fifth metatarsal at the metaphyseal-diaphyseal junction (Jones fracture)
  9. Peroneal tendon subluxation/dislocation
  10. Malleolar fracture
  11. Calcaneocuboid joint sprain

It is important to remember that in growing children the physis is much weaker than the ligaments and is therefore more likely to be injured. An adult with swelling and tenderness over the anterolateral ankle and lateral malleolus will most likely have an anterior talofibular ligament sprain. The child, however, will most likely have a physeal fracture.

Osteochondral fractures of the talar dome often accompany forceful inversion of the ankle. These fractures generally occur along the midlateral or posteromedial portion of the talar dome. With midlateral lesions, the patient experiences pain and tenderness along the anterior corner of the talar dome when the ankle is plantarflexed. With the posteromedial lesion, there is tenderness behind the medial malleolus as the ankle is dorsiflexed. If this injury is suspected, anteroposterior and mortise views taken with the talus placed in varying degrees of dorsiflexion and plantarflexion may help in making a diagnosis.

The following x-rays demonstrates a small lucent area in the superolateral corner of the talus representing and OCD. 

Ankle

The lateral tubercle of the posterior talar process may be fractured when the foot is inverted by avulsing the posterior talofibular ligament or by compression. These patients will have posterolateral ankle pain and discomfort during active flexion of the great toe since the flexor hallucis longus tendon moves over the fracture. Dorsiflexion of the ankle and palpation posterior to the lateral malleolus will reveal point tenderness over the posterior process. A lateral x-ray film of the ankle will usually demonstrate the fracture. It is important to distinguish this fracture from a nonunited os trigonum.

The lateral process of the talus can fracture with dorsiflexion and inversion of the foot. This injury is commonly seen in snowboarders. The size of the fragment can vary from a small avulsed chip to a large intra-articular fragment. This is the most commonly missed injury in the hospital emergency department because considerable pain and swelling over the lateral aspect of the ankle makes this look like a simple ankle sprain. This fracture can usually be seen on the standard ankle mortise view with the ankle in 30° to 45° of internal rotation.

The anterior process of the calcaneus can be fractured in 2 distinct ways. With a plantarflexion/ inversion injury, the bifurcate ligament is stretched, avulsing the anterior process and resulting in a small transverse fracture. On the other hand, compression injury causes a larger and often comminuted fracture of the anterior process that can involve the calcaneocuboid joint. The anterior process can be easily palpated 3 to 4 cm distal and slightly plantar to the lateral malleolus where there may be localized tenderness and swelling. The standard lateral view of the ankle often will reveal this fracture, but an oblique projection may be required to see it.

The base of the fifth metatarsal may be fractured with a plantarflexion/inversion injury as the peroneus brevis forcibly contracts to prevent ankle inversion, thereby avulsing a portion of the lateral tubercle. This fracture should be distinguished from the transverse fracture that occurs in the metaphyseal-diaphyseal region, typically referred to as a Jones fracture. While the avulsion fracture at the base of the fifth metatarsal has an excellent prognosis, the Jones fracture requires special care to optimize an excellent outcome.

Treatment

Once an accurate diagnosis has been made and more serious injury has been excluded, the lateral ankle sprain can be treated based on the grade of injury.

Grade 1 and Grade 2 injuries should be treated initially with ice, compression, and elevation to reduce swelling. The patient should then be placed in a thermoplastic air stirrup splint or an ankle brace so that protected weight bearing can be allowed.

Crutches are usually used for the first few days.  In the air stirrup, weight-bearing can begin quickly after the injury. Prolonged nonweight-bearing is to be avoided as it will lead to excessive swelling, stiffness and delayed recovery. 

Grade 2 injuries usually take longer than Grade 1 injuries to achieve pain-free weightbearing. Protected range of motion in the splint or brace is preferred to rigid immobilization with a cast because early mobilization following ligamentous injury stimulates collagen orientation and promotes healing, even though full strength of the injured ligamentous structure may not be achieved for several months.

Rehabilitation is started early in the acute phase and is primarily targeted at reducing swelling and pain. Limiting soft tissue effusion significantly improves healing and limits time from activity. After pain and swelling are controlled, the subacute phase of rehabilitation concentrates on increasing pain-free motion while beginning isometric exercises to prevent loss of strength. Once full pain-free motion has been established, strength is increased with isotonic and isokinetic exercises, and proprioceptive training is initiated. The final phase of rehabilitation focuses on sport-specific exercises directed at returning to full sports participation.

Grade 3 injuries (complete ligament ruptures with instability) may be treated nonoperatively. In fact, a randomized, prospective study comparing operative to nonoperative treatment of Grade 3 ankle sprains found that those patients managed nonoperatively returned to work faster with no difference in joint laxity noted 2 years postinjury. The only group for whom surgical treatment might be considered would be high-performance dancers because of the high demand placed on their ankles.

Grade 3 injuries are treated initially in a fashion similar to Grades 1 and 2 injuries, that is, with ice, compression, and elevation. Rather than placing the patient in an air stirrup initially, they are placed in a walking boot or short leg cast for 3 weeks, followed by placement in a functional ankle brace or thermoplastic air stirrup splint for an additional 3 weeks. The rehabilitative process is similar to that described for Grades 1 and 2 injuries after the patient is transferred from the walking boot to the functional ankle brace.

Chronic Pain

A significant number of patients will complain of persistent symptoms after initial assessment and treatment. A study of ankle sprains in West Point cadets noted residual symptoms in as many as 40% of ankles at 6 months after initial injury.

If the patient's primary complaint is pain, it is first important to make certain that the patient has been adequately rehabilitated, as this is the most common cause of persistent pain after ankle injury. Peroneal weakness is the most common finding in this group of patients.

If the patient has been adequately rehabilitated, then a careful search for previously undetected trauma should be undertaken. A repeat radiograph should be obtained to exclude an obvious fracture. Look for osteochondral fractures of the talus.

If these are negative, the clinician may wish to pursue further evaluation with magnetic resonance imaging, which can be helpful in detecting occult fractures as well as injuries to the tendons of the foot or ankle. The more common fractures that can be missed include a talar dome fracture, fracture of the lateral process of the talus, anterior process of the calcaneus fracture, or a navicular fracture. Tendon injuries include peroneal tendon rupture, peroneal tendon subluxation or dislocation, or posterior tibial tendon rupture. Less common are injuries to the anterior tibial tendon or the flexor hallucis longus tendon.

Other common causes of continued ankle pain following a sprain include soft tissue impingement in the antero-lateral gutter of the ankle. This may be due to scarring of the anterior-inferior tib-fib syndesmotic ligament or soft tissue trapped in the lateral gutter of the ankle mortise.

If, on the other hand, the patient's primary complaint is that of ankle instability, it is again important to make sure that the ankle has been adequately rehabilitated. If rehabilitation has been adequate and the patient complains of the ankle giving way or the inability to cut or pivot, consideration for operative reconstruction of the ankle should be undertaken.

Prevention

A number of strategies have been employed to prevent ankle sprains. These strategies include prevention of injury in ankles that have never been injured as well as in previously injured ankles. For many years, athletic tape was the mainstay of preventive treatment; however, recent studies have shown that while athletic tape does provide a 10% increase in maximal resistance to inversion moments, after ~40 minutes of vigorous exercise, tape provides insignificant levels of protection.

On the other hand, the use of semirigid ankle stabilizers has been shown to be efficacious in preventing ankle injuries. In a large prospective, randomized trial, the use of semirigid braces resulted in a significant reduction in injury in braced athletes compared with athletes who were not braced. In fact, nonbraced athletes had 3 times the risk of injury as those who were wearing braces. The brace, however, did not reduce the severity of injury in individuals who were injured while wearing the brace. These devices would seem to be a reasonable and inexpensive way of reducing both the incidence of ankle injury as well as associated morbidity.

Summary

Ankle injuries are the most common musculoskeletal injuries seen in active children and adults. A careful understanding of the anatomy and mechanisms of injury that are responsible for causing injury will allow the clinician to perform a directed history and physical examination to establish an accurate diagnosis. An understanding of concomitant injuries that can masquerade as an ankle sprain is critical, since exclusion of these injuries will result in significant reduction in morbidity and time lost from activity. Treatment of the uncomplicated ankle sprain should focus on early protected mobilization and aggressive rehabilitation, as this has been shown to provide the best outcome in terms of function and return to activity. In the patient who presents with persistent symptoms, a careful search for undetected fractures or soft tissue injuries should be undertaken. The persistently unstable ankle is best treated with surgical reconstruction in those patients who have undergone an appropriate course of treatment and rehabilitation.

Key Points

  • A carefully taken injury history will elicit the mechanism of injury and provide valuable clues as to the ligamentous structures that may be injured.
  • The physical examination should be systematic and thorough and should include careful observation of the ankle for swelling, deformity, and ecchymosis.
  • Before treatment can begin, an accurate diagnosis must be made. It is important to consider the differential diagnosis of the acutely injured ankle so that serious injury that may mimic an ankle sprain can be excluded.
  • After pain and swelling are controlled, the subacute phase of rehabilitation concentrates on increasing pain-free motion while beginning isometric exercises to prevent loss of strength.

References

  • Puffer J., Clinical Cornerstone 3(5):38-49, 2001, Excerpta Medica, Inc.

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